Apparatus for controlling recording and reproduction in digital video cassette tape recorder

Abstract: An apparatus for controlling recording and reproduction in a video cassette tape recorder capable of, in a recording mode, separating specific data for speed-varied reproduction from compressed digital video signals, recording them on designated tracks, recording position information of the designated tracks on a control track by an index head or recording position information of recording position-synchronized blocks at the starting portions of the designated tracks recorded with the specific data, and in a speed-varied reproduction mode, controlling a capstan servo speed so as to maintain the travel of a magnetic tape at a normal speed and periodically or non-periodically accelerate or decelerate it where specific data for varied-speed have been recorded periodically or non-periodically on predetermined portions of tracks, thereby making heads travel repeatedly at the normal speed and the high speed and thereby detect continuously the specific tracks for varied-speed. A repeatability of reproduced video at a varied speed is obtained without any deterioration in picture quality, because of recording of specific data for speed-varied reproduction and continuous detection of the specific data in the speed-varied reproduction.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a circuit for controlling recording and reproduction in a digital cassette tape recorder. Description of the Prior Art For analog/digital conversion for converting an analog video signal into a digital video signal and linear quantization, a signal transmission rate of about 100 Mega bits per second is typically required in the case of normal TV broadcast signal such as NTSC, SECAM and PAL signals. On the other hand, high definition TV (HDTV) signal with higher resolution than that of the normal TV broadcast signal requires a signal transmission rate higher than 100 Mega bits. For achieving data transmission in a limited transmission band, digitalized video signals should be transmitted in the form compressed in accordance with the video data compression-technique. In the case of digital cassette tape recorders (digital VCRs) having a limitation on record bandwidth, signals recorded on a magnetic tape may be digital, normal TV signals having the form of compressed signals or digital, HDTV signals having the form of compressed signals. Referring to FIG. 1, there is illustrated a conventional recording circuit for such a digital VCR. As shown in FIG. 1, the recording circuit includes an interface 1 for converting a compressed digital video signal into a signal having the recordable form, an interleaving and channel-dividing circuit 2 for interleaving an output V1 from the interface 1 in a predetermined form to reduce bursts error and channel-dividing it to be matched with the zero bandwidth of a recording channel, recording formatters 3A and 3B for respectively converting outputs V2 and V3 of the interleaving and channel-dividing circuit 2 to record formats each including a synchronous signal, an identification signal and redundancy bits for error correction codes, channel modulators 4A and 4B for modulating outputs V4 and V5 of the recording formatters 3A and 3B, respectively, recording amplifiers 5A and 5B for amplifying outputs V6 and V7 of the channel modulators 4A and 4B, respectively, a drum pulse generator 7 for outputting two pulses at every rotation of a head drum 6 caused by driving of a drum motor M1, and switches SW1 and SW2 for performing their switching operations based on an output SWP from the drum pulse generator 7 to selectively transmit outputs V8 and V9 of the recording amplifiers 5A and 5B to heads HD1 (or HD3) and HD2 (or HD4), respectively. In FIG. 1, the reference numeral 8 denotes a guide pin, 10 a pinch roller, and 9 a capstan adapted to be rotated by a capstan motor M2. FIG. 2 is a block diagram illustrating a conventional reproduction circuit for the digital VCR. As shown in FIG. 2, the reproduction circuit includes reproduction amplifiers 11A and 11B for receiving outputs from selected heads HD1 (or HD3) and HD2 (or HD4) mounted on the head drum 6 via the switches SW1 and SW2 switched in accordance with the output SWP from the drum pulse generator 7 and amplifying them, respectively, equalizers 12A and 12B for compensating distortions of frequency characteristics of outputs V10 and V11 of the reproduction amplifiers 11A and 11B, respectively, channel demodulators 13A and 13B for demodulating outputs V12 and V13 of the equalizers 12A and 12B, respectively, sync-detecting and error-correcting circuits 14A and 14B for detecting synchronous signals SYNC added in a recorded signal from the outputs V14 and V15 of the channel demodulators 13A and 13B and correcting errors of the outputs V14 and V15, respectively, deinterleaving circuits 15A and 15B for deinterleaving outputs V16 and V17 of the sync-detecting and error-correcting circuits 14A and 14B into the original signal form, respectively, a deformatter 16 for recovering outputs V18 and V19 of the deinterleaving circuits 15A and 15B to the original signal format, and an interface 17 for converting an output V20 of the deformatter 16 into a reproduced digital signal Vo and outputting it. Now, operations of the conventional circuits will be described in conjunction with FIGS. 1 to 6. First, in a recording mode, a compressed HDTV signal or compressed normal TV signal is applied to the interface 1 which, in turn, converts the received signal into a signal V1 capable of being recorded and reproduced. The signal V1 is then interleaved into a predetermined form to reduce burst errors in the interleaving and channel-dividing circuit 2 which, in turn, outputs signals V2 and V3 channel-divided so as to be matched with the bandwidth of the recording channel. The outputs V2 and V3 from the interleaving and channel-dividing circuit 2 are applied to the recording formatters 3A and 3B and then added with synchronous signals SYNC, identification signals ID and redundancy bits for error correction codes ECC in the recording formatters 3A and 3B. Resultant signals from the recording formatters 3A and 3B are then received in the channel modulators 4A and 4B which, in turn, output signals V6 and V7 matched with a predetermined recording format, respectively. The outputs V6 and V7 from the channel modulators 4A and 4B are applied to the recording amplifiers 5A and 5B which, in turn, amplify them, respectively. Outputs V8 and V9 from the recording amplifiers 5A and 5B are applied to selected heads HD1 (or HD3) and HD2 (or HD4) via the switches SW1 and SW2 switched by the output SWP from the drum pulse generator 7, so that they are recorded on a magnetic tape in a recording format shown in FIG. 3. In this case, the drum pulse generator 7 generates two pulses at every rotation of the head drum 6 driven by the drum motor M1. Meanwhile, frames have a mixed form of intra-frames (I-frames) able to be independently decoded and predictive frames (P-frames) compressed by moving information of previous screen and disable to be independently decoded, in accordance with a video compression system for HDTV signals or an MPEG (Moving Picture Experts Group) system. Bit rate generated in each frame is non-uniform, as shown in FIG. 5. In a reproduction mode, the magnetic tape travels by the rotation of the capstan 9 caused by the capstan motor M2 while being in contact with the head drum 6 rotating by the driving force of the drum motor M1. At this time, the heads HD1 (or HD3) and HD2 (or HD4) detect signals on the magnetic tape and send them to the reproduction amplifiers 11A and 11B via the switches SW3 and SW4 switched by the output SWP of the drum pulse generator 7, respectively. The signals received in the reproduction amplifiers 11A and 11B are amplified to a predetermined level and then sent to the equalizers 12A and 12B which, in turn, output signals V12 and V13 having compensated frequency characteristics, respectively. The signals V12 and V13 from the equalizers 12A and 12B are then applied to the channel demodulators 13A and 13B, respectively, so as to be demodulated. Outputs V14 and V15 from the channel demodulators 13A and 13B are received in the sync-detecting and error-correcting circuits 14A and 14B which, in turn, detect respectively synchronous signals SYNC and identification signals ID from synchronous block of the received signals and remove error components included in the data. Outputs V16 and V17 from the sync-detecting and error-correcting circuits 14A and 14B are applied to the deinterleaving circuit 15A and 15B which, in turn, deinterleave the signals V16 and V17 and thereby generate signals V18 and V19 having the original signal forms, respectively. The signals V18 and V19 are received in the deformatter 16 and thereby converted to the format having the signal form prior to the record. Signal V20 from the deformatter 16 is applied to the interface 17 which, in turn, generates a reproduced digital signal Vo. In speed-varied reproduction, the rotation speed of the head drum 6 is kept constant while the travel of the magnetic tape is accelerated. As a result, the heads HD1 to HD4 travel across tracks on the magnetic tape. The trace of the heads is shown in FIG. 3. Consequently, the detected signals have a discontinuous data form, namely, data burst with a magnitude inversely proportional to the travel speed of the magnetic tape. In the case of existing analog VCRs, data of one field are recorded in one track in the reproduction order. Accordingly, regions on tracks from which data are detected in the speed-varied reproduction mode are directly associated with reproduction regions of a corresponding screen. Therefore, video reproduction in the speed-varied mode is possible even when a noise bar is generated due to data detected on an adjacent track. In the case of existing digital VCRs, however, data of one field are recorded in a plurality of tracks, as shown in FIG. 3. As a result, reproduction bursts on adjacent tracks have no relation with the reproduction order. In this case, therefore, a frame memory and an addressing process for rearranging data detected are needed. Furthermore, there is a problem of an inevitable mosaic-shaped distortion of small segments due to discontinuous detection of data bursts. For video reproduction in the existing digital VCRs, data bursts detected should be independently decoded. However, these data bursts include unrecoverable other data on the screen or unrecoverable previous screen data, because the data-bursts have the digital form compressed using the correlation between signals that may be the important factor of adversely affecting the picture quality in reproduction. The unrecoverable data can not be decoded and thereby reproduced in the form of videos. In particular, such a problem becomes more frequent in the case of data obtained from the video compression system such as the variable length coding involving non-uniform data lengths. In other words, although data bursts detected from tracks on which data of the 0-th I-frame, the n-th I-frame, the 2n-th I-frame are recorded can be constructed to a video, data bursts detected from tracks on which data of P-frames are recorded can not be constructed to a video. Document EP-A-0 505 985 discloses an apparatus for controlling recording and reproducing in a VCR, comprising means for extracting I-frame specific data and means for varying the reproducing speed based on the index information of I-frames. The apparatus comprises frame extracting means for buffering and amplifying compressed digital data, input thereto; frame recording position controlling means for calculating the number of tracks for the compressed digital data, outputting the buffered and amplified compressed digital data, comprising I-frame specific data, and generating a multiplexing timing signal; frame position information recording means for recording position information of tracks for a speed-varied reproduction on a magnetic tape, based on said multiplexing timing signal; digital recording means for recording the buffered and amplified compressed digital data, comprising the I-frame specific data, on said magnetic tape; digital reproduction means for reproducing the I-frame specific data recorded on said magnetic tape; frame position information detecting means for detecting position information of specific tracks for the speed-varied reproduction; and tape speed controlling means for controlling the speed of a capstan motor, so that a normal-speed travel and a high-speed travel of the magnetic tape are performed by rotation of the capstan motor. SUMMARY OF THE INVENTION Therefore, an object of the invention is to provide an apparatus for controlling recording and reproduction in a digital VCR capable of, in a recording mode, extracting independently-decodable data, namely, intra-frames from digital signals having a compressed form so as to record them on tracks designated with respect to a speed multiple and, in a speed-varied reproduction mode, repeatedly performing a normal-speed travel and a high-speed travel of a magnetic tape so as to detect specific data for speed-varied reproduction periodically or non-periodically recorded on tracks of the magnetic tape, thereby reproducing videos with improved picture quality. In accordance with the present invention, this object can be accomplished by providing an apparatus for controlling recording and reproduction in a video cassette tape recorder according to claim 1. Other features are given in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantages of the invention will become more apparent upon a reading of the following detailed specification and drawings, in which: FIG. 1 is a block diagram of a conventional recording circuit for a digital VCR; FIG. 2 is a block diagram of a conventional reproduction circuit for a digital VCR; FIG. 3 is a schematic view illustrating recording tracks of a magnetic tape and a trace of heads travelling in a speed-varied reproduction mode in accordance with the prior art; FIG. 4 is a schematic view illustrating a correlation among frames in accordance with a video compression system; FIG. 5 is a schematic view illustrating an encoded bit stream; FIG. 6 is a schematic view illustrating synchronous blocks of a video signal for recording and reproduction; FIG. 7 is a block diagram of a recording control circuit for a digital VCR in accordance with the present invention; FIG. 8 is a block diagram of a reproduction control circuit for a digital VCR in accordance with the present invention; FIG. 9 is a schematic view illustrating recording tracks in accordance with the present invention; FIGS. 10A to 10D are waveform diagrams of signals generated in recording position control; FIG. 11 is a schematic view illustrating recording position-synchronized blocks in accordance with the present invention; FIG. 12 is a flow chart illustrating a frame detection procedure in accordance with the present invention; FIGS. 13A to 13C illustrate a capstan servo speed control in accordance with the present invention; and FIGS. 14A to 14D are waveform diagrams of signals generated in frame removal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 7 and 8, there is illustrated an apparatus for controlling recording and reproduction in a digital VCR in accordance with the present invention. FIG. 7 is a block diagram illustrating a recording control circuit device for a digital VCR in accordance with the present invention. As shown in FIG. 7, the recording control circuit device includes a frame extracting unit 20 for buffering and amplifying an output signal V1, namely, compressed digital data, of an interface 1, and extracting specific data for speed-varied reproduction from the received signal V1, a frame recording position controlling unit 21 for selectively outputting an output V22 of the frame extracting unit 20 obtained after the buffering and amplifying operations and the extracted specific data V23, and outputting a multiplexing timing signal V27', a frame position information recording unit 19 for recording track position information and index information for speed-varied reproduction on a magnetic tape, based on the multiplexing timing signal V27', and a digital recording unit for recording the digital data including the index information on the magnetic tape. Similar to the conventional case, the digital recording unit 18 includes an interleaving and channel-dividing circuit 2, recording formatters 3A and 3B, channel modulators 4A and 4B, recording amplifiers 5A and 5B, a head drum 6 equipped with heads HD1 to HD4, a drum pulse generator 7 and switches SW1 and SW2. With this construction, the digital recording unit 18 records digital signals including index signals on the magnetic tape. For simplicity of the description, detailed description concerning to the digital recording unit 18 will be omitted. The frame extracting unit 20 includes a buffer 22 adapted to buffer the output signal V1 of the interface 1 and thereby amplify it to a predetermined level, a frame detector 24 adapted to detect specific data corresponding to an intraframe, and a frame memory 23 adapted to store the detected specific data. The frame recording position controlling unit 21 includes a track number calculator 28 adapted to calculate the number of tracks, a multiplexing timing generator 27 adapted to operate an output SWP of the drum pulse generator 7 and thereby generate a multiplexing timing signal V27, a bit stuffing circuit adapted to make the output signal V23 of the frame memory 23 have a constant data length when the output signal V23 is at an underflow state, and a multiplexer 25 adapted to multiplex the output signals V22 and V23 of the frame extracting unit 20 and thereby output a signal V25. On the other hand, the frame position information recording unit 19 includes a frame position recorder 29 adapted to receive the multiplexing timing signal V27' from the frame recording position controlling unit 21 and record, on the leading portion of a track for varied speed, position information of a next track for speed change, and an index signal recorder 30 adapted to record index information of a track to be scanned by an index head 31. In FIG. 7, the reference numeral 8 denotes a guide pin, 9 a capstan engaged with a pinch roller 10, M1 a drum motor, and M2 a capstan motor. FIG. 8 is a block diagram illustrating a reproduction circuit device in accordance with the present invention. As shown in FIG. 8, the reproduction circuit includes a digital reproduction unit 32 for reproducing compressed digital data recorded on the magnetic tape, a frame position information detecting unit 33 for detecting index information from the magnetic tape and detecting information indicative of the position of a specific track, a tape speed controlling unit 34 for controlling the speed of the capstan motor M2, and a frame removing unit 35 for removing specific data for speed-varied reproduction during a reproduction at a constant speed. The digital reproduction unit 32 includes the head drum 6 equipped with the heads HD1 to HD4, the drum pulse generator 7, switches SW3 and SW4, reproduction amplifiers 11A and 11B, equalizers 12A and 12B, channel demodulators 13A and 13B, and sync-detecting and error-correcting circuits 14A and 14B. This construction of the digital reproduction unit 32 is similar to that of the conventional digital reproduction unit shown in FIG. 2. Therefore, detailed description concerning to the digital reproduction unit 32 will be omitted for simplicity of the description. The frame position information detecting unit 33 includes an index signal detector 36 adapted to detect index information, a recording position-synchronized block detector 40 adapted to detect, from the outputs V16 and V17 of the sync-detecting and error-correcting units 14A and 14B, position information of a specific track including specific data recorded, and a recording position decoder 39 adapted to decode the detected position information. The tape speed controlling unit 34 includes a capstan servo-speed calculating circuit 38 adapted to operate outputs V36 and V39 of the frame position information detecting unit 33, and a drive signal generator 37 adapted to generate a drive signal V37 for controlling the speed of the capstan motor M2. Finally, the frame removing unit 35 includes a frame removal timing generator 41 adapted to operate an output of the drum pulse generator 7 and outputs V36 and V39' of the frame position information detecting unit 33 and thereby generate a timing signal for removing specific data for speed-varied reproduction, a stuffing bit-detecting and removing circuit 42 adapted to detect and remove a stuffing bit added for preventing generation of the underflow of the frame memory 23, and a deformatter 16 adapted to convert an output of the digital reproduction unit 32 to the format having the signal form prior to the record. Operations of the apparatus for controlling recording and reproduction in the digital VCR in accordance with the present invention will be described, in conjunction with FIGS. 4 to 14. First, in a recording mode, an input signal Vi such as a compressed HDTV signal or compressed normal TV signal is applied to the interface 1 which, in turn, converts the received signal into a signal V1 having the form capable of being recorded and reproduced. The signal V1 from the interface 1 is then applied to the frame extracting unit 20. In the frame extracting unit 20, the received signal V1 is buffered and amplified by the buffer 22. By the buffering and amplifying operations, the signal V1 is delayed for a predetermined time. The frame detector 24 detects compressed I-frames repeated at intervals of n frames, from a bit stream encoded to have frames with different compressed bit lengths. The frame memory 23 stores data of the detected I-frames. In other words, compressed digital data of the I-frames repeatedly present at intervals of n frames are separated from the encoded bit stream shown in FIG. 4 and then duplicatively recorded on a specific track because they can be independently decoded. A write enable signal W/E of high level is applied to the frame memory 23 only for the period of detecting I-frames from the encoded bit stream by the frame detector 24. As a result, the frame memory 23 can store only the compressed video data of the I-frames. This procedure for detecting I-frames will be described in detail, in conjunction with FIG. 12. An input bit stream is received in the frame detector 24 and then decoded. The frame detector 24 detects a frame mark code from a header of each frame in the bit stream. When the frame mark code is detected, an increment in frame counted value is carried out. Where I-frames are present at intervals of n frames, the number of counted frames is compared with the number of repeated I-frames. When a 2K-th frame mark code (K = 0, 1, 2, .....) is detected by the comparison, a write enable signal W/E of high level is applied to the frame memory 23, thereby enabling compressed digital data bits of a corresponding I-frame to be stored. When a next frame mark code is detected, a write enable signal W/E of low level is applied to the frame memory 23. As a result, it is possible to prevent frames of the frame bit stream other than I-frames from being stored. The frame recording position controlling unit 21 sends selectively I-frame data V23 and record data V22 outputted from the frame extracting unit 20 to the digital recording unit 18 at a predetermined timing. Accordingly, a recording format shown in FIG. 9 is formed in the digital recording unit 18. On the other hand, since lengths of compressed data of frames are non-uniform, the frame memory 23 may encounter an underflow phenomenon that data stored in the frame memory 23 at the moment an I-frame is recorded in the frame memory 23 is insufficient or an overflow phenomenon that data stored in the frame memory 23 prior to recording of an I-frame is full. This will be described in detail. Assuming that the average bit rate of input data received in the interface 1 is R and the size of regions of the input data occupied by I-frames is a, the average bit rate of data to be recorded is expressed by R + αR. This average bit rate of data is calculated in the track number calculator 28. In this case, α can be calculated from α = the number of tracks, i, for I-frames/ the number of tracks, j, for P-frames. Here, the number of tracks, i, is generally determined by the average bit rate of I-frames. The multiplexing timing generator 27 operates an output V28 of the track number calculator 28 which calculates the number of tracks, i, and the number of tracks, j. The multiplexing timing generator 27 also operates the output SWP of the drum pulse generator 7. By these operations, a reference pulse is calculated. One pulse of the output SWP of the drum pulse generator 7 corresponds to a recording period for one track in a case of recording one-channel data and to a recording period for two tracks in a case of recording two-channel data. Accordingly, the multiplexing timing generator 27 outputs a switching signal V27 enabling the multiplexer 25 to selectively output data V23 for double speed stored in the frame memory 23 and normally-recorded data (FIG. 10B) buffered and amplified by the buffer 22, as shown in FIG. 10D. In the output V22 from the buffer 22 shown in FIG. 10B, Δt represents the period for delaying outputting of I-frames present between the first recording track and a predetermined track so as to prevent an underflow phenomenon. In the worst case where an underflow phenomenon occurred in the frame memory 23, the bit stuffing unit 26 performs a bit stuffing operation for adding, to data of I-frames, escape synchronous codes and dummy bits capable of being detected in reproduction, so as to make the data have a constant length. On the other hand, where an overflow phenomenon occurred in the frame memory 23, a write enable signal W/E of low level is applied from the frame detector 24 to the frame memory 23 for a predetermined period. In the frame position information recording unit 19, the frame position recorder 29 and the index signal recorder 30 receive the output V27' from the multiplexing timing signal generator 27 of the frame recording position controlling unit 21. The frame position recorder 29 outputs information V29 based on its frame position discrimination to the recording formatters 3A and 3B. Based on the information V29, the recording formatters 3A and 3B form a synchronous block including information indicative of the position of a track including a next I-frame recorded, in each video data region. The recording formatters 3A and 3B also record the recording position information in the first synchronous block recording position of the tracks including I-frames recorded, as shown in FIG. 9. Here, the recording position information represents the code converted from the number of tracks present between the track including the current I-frame recorded and the track including the next I-frame recorded, as shown in FIG. 11. On the other hand, the index signal recorder 30 outputs index information V30, namely, a pulse indicative of whether an I-frame has been recorded or not, to the index head 31 which, in turn, records the index information V30 on a control track. The above-mentioned overall operations will be described in detail. As the head drum 6 carrying the heads HD1 to HD4 is rotated by the driving force of the drum motor M1 while the magnetic tape engaged between the capstan 9 and the pinch roller 10 is fed by the driving force of the capstan motor M2, the interface 1 receiving the input signal Vi such as the compressed HDTV signal or the normal TV signal applies its output V1 to the frame extracting unit 20. Thereafter, the recorded data is buffered and amplified in the buffer 22 for a predetermined period while the I-frame data is stored in the frame memory 23 in accordance with the write enable signal W/E from the frame detector 24. Subsequently, the multiplexer 25 receives selectively the output V22 from the buffer 22 and the output V23 from the frame memory 23, based on the output V27 from the multiplexing timing generator 27. As a result, the multiplexer 25 outputs the output signal V25 shown in FIG. 10 to the digital recording unit 18. Thereafter, the interleaving and channel-dividing circuit 2 of the digital recording unit 18 interleaves the signal V25 to a predetermined form for reducing burst errors and then outputs signals V2 and V3 channel-divided to be matched with a recording channel bandwidth, to the recording formatters 3A and 3B, respectively. Accordingly, the recording formatters 3A and 3B form synchronous blocks shown in FIG. 6 so as to add synchronous signals SYNC, identification signals ID and error correction codes ECC. The recording formatters 3A and 3B also form position information blocks of recording tracks, based on the output V29 from the frame position recorder 29 in the frame position information recording unit 19, thereby forming position information about the first synchronous blocks of the tracks including I-frames recorded. Outputs V4 and V5 are converted to a predetermined recording format in the channel modulators 4A and 4B, amplified to a predetermined level by the recording amplifiers 5A and 5B, and then selectively sent to the heads HD1 (or HD3) and HD2 (or HD4) via the switches SW1 and SW2 switched by the output SWP of the drum pulse generator 7 generated by the rotation of the drum motor M1. Thus, the outputs of the recording amplifiers 5A and 5B selectively applied to the heads HD1 (or HD3) and HD2 (or HD4) via the switches SW1 and SW2 being switched are recorded on the magnetic tape in a recording format shown in FIG. 9. On the other hand, when a speed-varied reproduction mode is selected in a case that data of the recording format shown in FIG. 9 has been recorded on the magnetic tape, the data recorded on the magnetic tape is reproduced in the digital reproduction unit 32. That is, signals recorded on the magnetic tape are detected by the heads HD1 (or HD3) and HD2 (or HD4) while the magnetic tape engaged between the capstan 9 and the pinch roller 10 rotated by the capstan motor M2 travels on the head drum 6 driven by the drum motor M1. The signals detected by the heads HD1 (or HD3) and HD2 (or HD4) are sent to the reproduction amplifiers 11A and 11B via the switches SW3 and SW4 switched by the output SWP of the drum pulse generator 7, respectively. The signals received in the reproduction amplifiers 11A and 11B are amplified to a predetermined level and then sent to the equalizers 12A and 12B which, in turn, compensate distortions of frequency characteristics of the amplified signals V10 and V11, respectively. Resultant signals V12 and V13 from the equalizers 12A and 12B are then applied to the channel demodulators 13A and 13B which, in turn, demodulate the output signals V12 and V13 to the original signal forms, respectively. Output signals V14 and V15 from the channel demodulators 13A and 13B are received in the sync-detecting and error-correcting circuits 14A and 14B which, in turn, detect respectively synchronous signals SYNC and identification signals ID from the received signals V14 and V15 and remove error components included in the recorded data. Resultant signals V16 and V17 from the sync-detecting and error-correcting circuits 14A and 14B are applied to the deinterleaving circuits 15A and 15B which, in turn, deinterleave the signals V16 and V17 to the original signal forms, respectively. Resultant signals V18 and V19 are then sent to the deformatter 16 of the frame removing unit 35. At this time, the frame position information detecting unit 33 detects index information recorded on a control track disposed at the lower edge of the magnetic tape by the index head 31. The index information is a pulse indicative of a track including an I-frame. On the other hand, the recording position-synchronized block detector 40 detects recording position-synchronized blocks recorded with I-frames from the outputs V16 and V17 of the sync-detecting and error-correcting circuits 14A and 14B. Upon detecting the index information in order to achieve a discrimination for the position of a specific track, the index signal detector 36 takes into consideration the time taken to control a speed matched with a speed multiple and calculated in the capstan servo speed calculator 38 of the tape speed controlling unit 34. The physical position of the index head 31 is determined by the processing speed of the capstan servo speed calculator 38. The recording position-synchronized block detector 40 also detects the outputs V16 and V17 of the sync-detecting and error-correcting circuits 14A and 14B and separates recording position-synchronized blocks shown in FIG. 11 from the detected signals V16 and V17. The recording position-synchronized block detector 40 outputs a signal 40 which is indicative of codes relating to the speed multiple and selected from codes indicative of relative positions and present in the separated synchronous blocks. The recording position decoder 39 decodes the signal V40 received from the recording position-synchronized block detector 40 and the speed multiple n. An optional code DIFi present in each synchronous block is a code indicative of the number of tracks present between the current track and the i-th track including specific data recorded. Accordingly, the frame position information detecting unit 33 detects specific track position information periodically or non-periodically recorded and track position information about I-frames recorded in the recording position-synchronized blocks, taking into consideration the calculation time taken to control the speed of the capstan motor M2 and the driving time. In this connection, the capstan servo speed calculator 38 receives the position information V36 from the index signal detector 36 and the position information V39 from the recording position decoder 39 and thereby calculates the rotation speed of the capstan motor M2 in accordance with the input speed multiple n. Resultant signal V38 from the capstan servo speed calculator 38 is then applied to the capstan servo driving signal generator 37 which, in turn, controls the speed of the capstan motor M2 so that the capstan motor M2 can be driven repeatedly at a normal speed and a high speed. As a result, the heads HD1 to HD4 mounted on the drum 6 perform repeatedly a travel at the normal speed on specific tracks of the magnetic tape and a jumping travel on other tracks, thereby enabling reproduction of speed-varied videos. FIGS. 13A to 13C illustrate an example of a capstan servo speed control in a case where speed-varied specific data have been recorded on every two-track at intervals of four tracks. In this case, the capstan motor M2 is driven two tracks at a normal speed in the same direction as the recording tracks for first half of the initial cycle shown in FIG. 13B. For next half of the initial cycle, the capstan motor M2 is driven four tracks at a high speed. During the accelerated driving, the capstan motor M2 exhibits the driving characteristic shown in FIG. 13A because the output V37 of the capstan servo driving signal generator 37 is periodically varied in level, as shown in FIG. 13C. By virtue of such a speed-varied driving of the capstan motor M2, therefore, it is possible to reduce an excessive characteristic of the capstan servo speed. The outputs V18 and V19 from the digital reproduction unit 32 resulted from the speed-varied reproduction are sent to the deformatter 16 of the frame removing unit 35, converted into the signal form prior to the recording, and then outputted as a speed-varied reproduced signal Vo such as a digital HDTV signal or a normal TV signal via the interface 17. For the signal conversion in the deformatter 16, it is required to remove the stuffing bits or dummy bits added for preventing the underflow phenomenon of the frame memory 23 upon recording data for varied speed on specific tracks. To this end, the stuffing bit-detecting and removing circuit 42 supplies a bit removing signal V42 for preventing any bit string from being outputted to the interface 17 when a stuffing synchronous code recorded at the starting portion of stuffing bits is detected. The supplying of the bit removing signal V42 is continued until a stuffing bit end code is detected. In the reproduction at the normal speed, the frame removing unit 35 also separates data of recording tracks for varied speed so that the I-frame data recorded on the magnetic tape for the speed-varied reproduction is prevented from being outputted to the interface 17 and thereby being included in the reproduced signal Vo. On the other hand, the frame removal timing generator 41 receives position information of tracks recorded with specific data for varied speed from both the recording position decoder 39 and the index signal detector 36 of the frame position information detecting unit 33. Based on the output SWP of the drum pulse generator 7 shown in FIG. 14A, the frame removal timing generator 41 then outputs a frame removing signal V41 shown in FIG. 14C to the deformatter 16. Based on the frame removing signal V41, the deformatter 16 removes I-frame data from the signals V18 and V19 (FIG. 14B) received from the deinterleaving circuits 15A and 15B of the digital reproduction unit 32. As a result, the deformatter 16 outputs a signal V20 shown in FIG. 14D, thereby enabling the reproduction at the normal speed. As apparent from the above description, the present invention provides an apparatus for controlling recording and reproduction in a magnetic VCR capable of separating specific data for speed-varied reproduction from compressed digital video signals and recording them on designated tracks in a recording mode, recording position information of the designated tracks on a control track by an index head or recording position information of recording position-synchronized blocks at the starting portions of the designated tracks recorded with the specific data so as to accurately scan the designated tracks in a reproduction mode, controlling a capstan servo speed so as to maintain the travel of a magnetic tape at a normal speed and periodically or non-periodically accelerate or decelerate it where specific data for varied-speed have been recorded periodically or non-periodically on predetermined portions of tracks, thereby making heads travel repeatedly at the normal speed and the high speed and thereby detect continuously the specific tracks for varied-speed. In accordance with the apparatus, the specific data for speed-varied reproduction is removed in the reproduction at the normal speed. Thus, the reproduction at the normal speed can be accomplished. Accordingly, the present invention provides a repeatability of reproduced video at a varied speed without any deterioration in picture quality in that it enables recording of specific data for speed-varied reproduction and continuous detection of the specific data in the speed-varied reproduction.

Claims: An apparatus for controlling recording and reproducing in a video cassette tape recorder, comprising: frame extracting means (20) for buffering and amplifying compressed digital data input (V1) thereto, and extracting, from said compressed digital data (V1), I-frame specific data (V23) for a speed-varied reproduction; frame recording position controlling means (21) for calculating the number of tracks for the compressed digital data, selectively outputting the extracted I-frame specific data from said frame extracting means and the buffered and amplified compressed digital data (V22), and generating a multiplexing timing signal (V27'); frame position information recording means (19) for recording position information of tracks for a speed-varied reproduction on a magnetic tape and for recording index information of I-frames for the speed-varied reproduction on a control track of the magnetic tape by an index head, based on said multiplexing timing signal (V27'), wherein said index information indicates the position of tracks recorded with said I-frame specific data; digital recording means (18) for recording said extracted I-frame specific data and the buffered and amplified compressed digital data on said magnetic tape; digital reproduction means (32) for reproducing said extracted I-frame specific data recorded on said magnetic tape; frame position information detecting means (33) for detecting said index information of frames recorded on the control track for the speed-varied reproduction and for detecting position information of specific tracks for the speed-varied reproduction; tape speed controlling means (34) for controlling the speed of a capstan motor (M2), based on said detected index information, so that a normal-speed travel and a high-speed travel of the magnetic tape are repeatedly performed by rotation of the capstan motor, whereby, in a speed-varied reproduction, the magnetic tape is maintained at a normal speed where the I-frame specific data for speed-varied reproduction have been recorded periodically or non-periodically on predetermined portions of tracks and periodically or non periodically accelerated or decelerated; and frame removing means (35) for removing the I-frame specific data in the reproduction at normal speed and for receiving an output from the digital reproduction means (32) and removing unnecessary bit streams from the extracted I-frame specific data during the speed-varied reproduction. An apparatus in accordance with claim 1, wherein said frame extracting means (20) comprises: a buffer (22) adapted to buffer an output (V1) of said interface and thereby amplify it for a predetermined period; a frame detector (24) adapted to detect said specific data from said output of the interface and output a write enable signal; and a frame memory (23) adapted to select and store the specific data, based on said write enable signal. An apparatus in accordance with claim 2, wherein said frame detector (24) is adapted to count the number of frames when a frame mark code is detected from a bit stream of said output of the interface, and to enable said write enable signal when said counted number of frames is determined to be the same as the number of specific frames repeated. An apparatus in accordance with claim 1, wherein said frame recording position controlling means (21) comprises: a track number calculator (28) adapted to operate an average bit rate of said compressed digital signals and size of the specific data, thereby calculating the number of tracks for the specific data and the number of tracks present between specific tracks; a multiplexing timing generator (27) adapted to receive an output from said track number calculator and output a switching signal for positioning the specific data on said specific tracks in accordance with a head switching signal; a multiplexer (25) adapted to select an output from said frame extracting means, based on an output from said multiplexing timing generator and sending it to said digital recording means; and a bit stuffing circuit adapted to fill insufficient data with bit streams or dummy bits when said output of the frame extracting means is at an underflow state. An apparatus in accordance with claim 1, wherein said tape speed controlling means comprises: a capstan servo speed calculator adapted to calculate a capstan servo speed for repeating a normal speed travel and a high speed travel on specific tracks in a speed-varied reproduction of specific track position information and track position information for specific data from said frame position information detecting means based on a speed multiple; and a capstan servo drive signal generator adapted to control driving of said capstan motor, based on an output of said capstan servo speed calculator. An apparatus in accordance with claim 1, wherein said frame removing means comprises: a deformatter adapted to convert said output of said digital reproduction means to a signal form prior to recording; a stuffing bit-detecting and removing circuit adapted to output a bit removing signal to said deformatter and thereby remove stuffing bits or dummy bits added for preventing generation of an underflow of said frame extracting means in the speed-varied reproduction; and a frame removal timing generator adapted to receive said specific track position information from said frame position information detecting means and output a frame removing signal to the deformatter, based on a head switching signal, thereby preventing outputting of said specific data for the varied speed in a normal-speed reproduction.

Inventors: KIM SOO KYUNG, LEE JE HYUNG, WOO SANG JOON, YANG TAE SEOK, KIM, SOO KYUNG, LEE, JE HYUNG, WOO, SANG JOON, YANG, TAE SEOK
Applicants: LG ELECTRONICS INC, LG ELECTRONICS INC.
Application year: 1994
Main classification: H04N5
IPC codes: G11B5, G11B15, H04N5, G11B20, G11B27, H04N9